The air pollution problems inherent in the operation of gasoline fueled and diesel oil fueled internal combustion engines are well known. For this reason various emission control devices are presently in use, and may be required by federal regulations in order to reduce the amount of pollutants discharged into the atmosphere by internal combustion engines. These emission control devices, however, only remove a portion of the pollutants and are subject to deterioration with the passage of time. Also, they often hinder engines from operating at peak efficiencies.
Natural gas is also sometimes used as a fuel for internal combustion engines. It has the capability of producing less combustion pollutants and decreasing engine operating costs without complex emission control devices, and its use reduces the rate of world fossil fuel consumption.
Since the current transportation infrastructure does not include large numbers of widely disbursed retail suppliers of natural gas for vehicles, it has been impractical to produce vehicles that are fueled solely by gaseous fuels like natural gas due to range limitations. It is more practical to equip vehicles with a supply of both a liquid fuel such as gasoline or diesel fuel and an auxiliary supply of gaseous fuel such as natural gas. To do that efficiently it is preferred that as little retrofitting be done as possible to existing fuel intake systems and configurations.
Various systems had been developed for mixing gaseous fuels with liquid fuels. For example, systems have been designed which entrain gaseous fuel through a gas metering valve into air supplied to the air inlet manifold of a diesel engine. This combination of air and fuel is then mixed with the diesel fuel prior to combustion. Exemplary of this type of system is that shown in U.S. Pat. No. 4,463,734. Since these systems control the flow of gaseous fuel by the volume of air entering the engine, there is a direct and constant gaseous fuel to diesel fuel ratio. However, because different load conditions can occur at various engine speeds, this type of system does not always provide a mixture which results in maximum efficiency.
U.S. Pat. No. 5,370,097, which is incorporated herein by reference, discloses a system for controlling the flow of gaseous fuel and the flow of liquid fuel into an internal combustion engine to increase efficiency and output.